mechanism, but a random numbers table was used to determine
allelic frequencies rather than considering individual matings.
Thus, I developed the following classroom activity that can be used
in middle school, high school, and postsecondary settings.
In the project, students conduct manual simulations using hypothetical organisms and alleles. In these simulations, there is a species of
interest in which the population in each generation is four individuals and generations do not overlap. There is a single locus of interest,
with two alleles: A1 and A2. Each group of four students is provided
with a data sheet (Figure 1), a six-sided die, a coin, and instructions
explaining the following parameters:
1. Each group member will represent a single member of the
population (Individual 1, 2, 3, or 4) and will retain their
assigned identity every generation.
2. The simulation will start with every individual being heterozygous (A1, A2).
3. In each generation, there will be four matings to yield four offspring for the next generation. The matings will be determined
via four rolls of a standard six-sided die, where the result of
each roll specifies a mating pair using the scheme shown in
Table 1. Because this is a random process, it is possible that
there will be more than one mating of a single type in a given
4. Homozygous individuals will only have a single allele to pass
on, whereas heterozygous individuals will need to determine
the allele passed on in the gamete following meiosis via a
coin flip: heads = A1 and tails = A2. Given that all individuals
start as heterozygous in generation 1, the first iteration will
require two coin flips for each of the four matings. In subse-
quent generations, matings may require two, one, or zero
coin flips, depending on the genotypes of the individuals.
5. Starting in generation 2, the genotype of an individual is determined by the outcome of the corresponding mating from the
previous generation. For example, individual 1 in generation
2 is the offspring of mating 1 from generation 1.
6. The matings continue until (a) one allele is fixed and the other
is lost, (b) n generations have elapsed, or (c) a set time has
elapsed. In an introductory undergraduate course for biology
majors, I found that it took ~45 minutes for all groups to complete the project, with allele loss/fixation or 20 generations
elapsed as the end point.
7. Upon completion, groups enter their allele frequencies for
either A1 or A2 on a spreadsheet, from which a graph of allelic frequency over generational time among the simulations
(Figure 2) can be produced.
Reflections, Revisions & Extensions
Our simulations were done in groups of four students, and we
noted the following points. First, doing the first generation’s matings class-wide would improve efficiency. A number of students
were uncertain and raised questions about the first iteration of
the simulation but were confident for all subsequent iterations.
Because of the random nature of genetic drift, the duration of a
given simulation is unpredictable. We had one group with an allele
Figure 1. A sample data sheet. The items in bold are entered in the sheet prior to distribution to students. This sheet shows the
results from one group simulation.